HFCs are of particular interest as potential replacements for highly useful, yet environmentally undesirable, chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs). Unlike CFCs and HCFCs, HFCs do not contain chlorine and therefore do not decompose to form chlorine-containing chemical species, which are suspected of causing depletion of the ozone layer. While HFCs thus avoid the main disadvantage of such chlorine-containing compounds, they nevertheless possess many of the beneficial properties of those compounds. For example, HFCs have been used successfully in place of HCFCs and CFCs as heat transfer agents, blowing agents, and propellants. Thus, HFCs are desirable targets of chemical synthesis.
Unfortunately, known methods for forming HFCs generally use as starting materials highly-halogenated alkanes and alkenes, such as, for example, hexafluoropropene, hexafluoropropane and 2-chloroheptafluoropropene. For example, U.S. Pat. No. 5,399,795--Franz et al discloses a method of making 1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea) in which hexafluoropropene is used as the starting material and is reacted with hydrogen fluoride (HF) to form the desired HFC. U.S. Pat. No. 5,780,6791, Tung et al. discloses a process which uses hexafluoropropane as a starting material to form HFC-227ea.
The present inventors have come to appreciate that such prior processes are disadvantageous for several reasons. One such disadvantage is that highly-halogenated compounds, when used as starting materials, tend to be very expensive. For example, hexafluoropropane at present costs about $6.00 per pound. Another disadvantage is that these prior art processes are not flexible and produce only HFC-227ea as a sole product. No useful intermediates or by-products are co-produced. Thus, the HFC-227ea produced by the prior art processes have relatively high operating costs, as well as relatively high capital costs.
Recognizing these and other drawbacks of the prior art, the present inventors have perceived a need for a new, efficient and more desirable method for producing a wide range of HFCs. These and other objects are achieved by the present invention as described below.